An important aspect of modern material handling is the development of mechanical readers for determining the nature of an article and subsequently directing it to its proper destination. One method of providing such a mechanical identification system is shown in the Dunigan et al patent No. 3,227,886, issued Jan. 4, 1966, wherein a retro-reflective pattern of spots is placed on a standard material container and a series of photocells can "read" the pattern. An important aspect of the Dunigan patent involves the provision of a series of retro-reflective indicating means which are slidable in a series of tracks which are parallel to the direction of motion of the container. Each indicating means can be selectively locked in one of a series of discrete locations along the length of the track, but can also be rendered slidable along the track to change location. In the Dunigan patent, the indicating means is spring-loaded outwardly of the track to engage a notch in the outer edge of the track. The system must satisfy two competing requirements: first, the indicating means must be smoothly and easily moved among the various discrete locations when movement is desired and, secondly, the indicating means must be positively locked against movement due to the physical shocks which normally occur in material handling. Although a properly-manufactured version of the Dunigan design functions quite well in these respects, inexpensive versions of the design have proved unsatisfactory.
Various alternative designs of the basic structure have been attempted in order to avoid manufacturing difficulties. For example, in one design the indicating means is placed in a smoothly slidable track, the bottom of the track being composed of an elongated strip of magnetized metal having closely-spaced alternations of magnetic pole along its length. The indicating means is also a magnet with the North-South poles arranged parallel to the length of the track. The result is that the indicating means is alternately attracted and repulsed as it moves along the length of the track. Thus, the indicating means can be pushed along the length of the track, but will normally be magnetically held in one of several discrete locations. Although this design does overcome some manufacturing problems of other designs, it has some material-economics problems of its own and the indicating means has a tendency to change position when exposed to extreme physical shock. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
It is, therefore, an outstanding object of the invention to provide a signal device for providing an easily changeable, machine-readable indicia on an object.
Another object of this invention is the provision of a signal device which can be easily deliberately changed when desired, but which will not change accidentally even when exposed to extreme physical shock.
A further object of the present invention is the provision of a signal device which is simple in construction, inexpensive to manufacture, and capable of along life of useful service.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.